Inkjet ink binder and inkjet ink composition

ABSTRACT

An inkjet ink binder including an aqueous dispersion of polymer particles, the polymer including, as polymerized units, (a) from 0 to 1 wt. % monoethylenically unsaturated acid monomer, based on polymer weight; and (b) monomer of the formula 
 
CH 2 ═C(R1)—CON(R2)(R3) 
 
wherein R1═H, CH 3  or C 2 H 5  and R2 and R3 are independently selected from C1-C6 saturated alkyl and cycloalkyl groups; and wherein the total of (a) and (b) is at least 0.1 wt % monomer based on the polymer weight. The binder may be a copolymer of ethyl acrylate and acrylamide. An inkjet ink composition including the inkjet ink binder, a colorant, and a liquid medium is also provided.

This invention relates to a binder composition for inkjet inks andinkjet inks including the binder. In particular, this invention relatesto an inkjet ink binder including an aqueous dispersion of polymerparticles, the polymer including, as polymerized units, (a) from 0 to 1wt. % monoethylenically unsaturated acid monomer, based on polymerweight; and (b) monomer of the formulaCH₂═C(R1)—CON(R2)(R3)wherein R1═H, CH₃ or C₂H₅ and R2 and R3 are independently selected fromC1-C6 saturated alkyl and cycloalkyl groups; and wherein the total of(a) and (b) is at least 0.1 wt % monomer based on the polymer weight. Inaddition the invention relates to an inkjet ink composition includingthe inkjet ink binder, a colorant, and a liquid medium.

In particular, this invention relates to inkjet inks having binderresins to fix pigments in the ink on the paper or other substrate onwhich the ink is applied. Such inkjet inks may be applied by standardthermal drop-on-demand printing.

U.S. Pat. No. 6,646,024 B2 discloses a polymeric binder useful forwater-resistant inkjet inks wherein the binder contains an acidcomponent in the range from about 1 to about 10 wt % of the polymer, aTg in the range from about −20° C. to about 25° C., and an averageparticle diameter in the range from about 250 to about 400 nm, and aparticle size distribution such that essentially all the particles havea diameter in the range from 130 to 450 nm. Wet-rub smear of printsformed from these inks or resistance to smearing by highlighter pens wasmuch improved over example inks not containing binder. The binder ofthis invention showed good printing reliability in the presence ofpolymer-dispersed pigments, but did not show good printing reliabilitywhen used with a self-dispersed pigment. Improvements in printingreliability in the presence of either polymer-dispersed and/or selfdispersed pigments and improved resistance to smearing by highlighterpens are still desired.

US Patent Application No. 20030176532 A1 discloses a polymeric binderuseful for water-resistant inkjet inks wherein the binder containsmethylol (meth)acrylamide or substituted methylol (meth)acrylamides.These moieties are reactive, and may form covalent bonds at roomtemperature liberating by-products such as formaldehyde (more rapidlywith heat and with catalysts) to form crosslinked polymer.

It is therefore desirable to obtain an inkjet ink binder which, whenincorporated into an inkjet ink, simultaneously provides printingreliability along with wet-rub smear resistance and resistance tosmearing by highlighter pens in a variety of ink formulations withoutthe evolution of by-products. The inkjet binder of the presentinvention, when incorporated into inkjet inks, provides suchperformance.

According to a first aspect of the present invention there is providedan inkjet ink binder comprising an aqueous dispersion of polymerparticles, said polymer comprising, as polymerized units, (a) from 0 to1 wt. % monoethylenically unsaturated acid monomer, based on polymerweight; and (b) monomer of the formulaCH₂═C(R1)—CON(R2)(R3)

wherein R1═H, CH₃ or C₂H₅ and R2 and R3 are independently selected fromH and C₁-C6 saturated alkyl and cycloalkyl groups; and wherein the totalof (a) and (b) must be at least 0.1 wt % based on said polymer weight.

According to a second aspect of the present invention there is providedan inkjet ink composition comprising the inkjet ink binder of the firstaspect of the present invention, a colorant and a liquid medium.

The present invention relates to an inkjet ink binder including anaqueous dispersion of polymer particles, the polymer including, aspolymerized units, (a) from 0 to 1 wt. % monoethylenically unsaturatedacid monomer, based on polymer weight; and (b) monomer of the formulaCH₂═C(R1)—CON(R2)(R3)

wherein R1═H, CH₃ or C₂H₅ and R2 and R3 are independently selected fromH and C1-C6 saturated alkyl and cycloalkyl groups; and wherein the totalof (a) and (b) must be at least 0.1 wt % based on said polymer weight.

Suitable acid monomers include, for example, acrylic acid, methacrylicacid, crotonic acid, itaconic acid, fumaric acid, maleic acid,monomethyl itaconate, monomethyl fumarate, monobutyl fumarate, sodiumvinylsulfonic acid, and acrylamidopropane sulfonic acid. Precursormonomers which form acid monomers before, during, or afterpolymerization such as maleic anhydride and sodium vinylsulfonates arealso included. Preferred acid monomers are carboxylic acid monomers suchas methacrylic acid, acrylic acid, and combinations thereof.

Suitable monomers of the formulaCH₂═C(R1)—CON(R2)(R3)wherein R1═H, CH₃ or C₂H₅ and R2 and R3 are independently selected fromH and C1-C6 saturated alkyl and cycloalkyl groups include(meth)acrylamide, ethacrylamide, N-methyl acrylamide, N-ethylmethacrylamide, N-t-butyl acrylamide, N,N-dimethyl acrylamide,N-cyclohexyl acrylamide, and the like. Expressly excluded are monomerswherein any of R1, R2, and R3 include functional moieties capable ofchemical reaction such as —OH, —CH₂OH, halogen, and —CHO, for example.

The polymer of the inkjet ink binder may also include a copolymerizedethylenically unsaturated third monomer other than the monomers recitedabove such as, for example, (meth)acrylic ester monomers includingmethyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate,decyl acrylate, lauryl acrylate, methyl methacrylate, butylmethacrylate, isodecyl methacrylate, lauryl methacrylate, hydroxyethylmethacrylate, hydroxypropyl methacrylate; (meth)acrylonitrile;amino-functional and ureido-functional monomers; monomers bearingacetoacetate-functional groups; styrene and substituted styrenes;butadiene; fluoro(meth)acrylates; ethylene, propylene, α-olefins such as1-decene; vinyl acetate, vinyl butyrate and other vinyl esters; andvinyl monomers such as vinyl chloride, vinylidene chloride. Preferred isfrom 10 to 98 wt % C1-C3 alkyl acrylate, based on polymer weight. Morepreferred is from 50 to 97% ethyl acrylate, based on polymer weight.

The aqueous emulsion polymer may contain from 0 to 5%, by weight basedon the dry weight of the copolymer, copolymerized multi-ethylenicallyunsaturated monomers such as, for example, allyl methacrylate, diallylphthalate, 1,4-butylene glycol dimethacrylate, 1,2-ethylene glycoldimethacrylate, 1,6-hexanediol diacrylate, and divinyl benzene.Preferred is the use of no copolymerized multi-ethylenically unsaturatedmonomers.

The glass transition temperature (“Tg”) of the emulsion copolymer istypically from −40° C. to 120° C., or from −20° C. to 80° C. or evenfrom −20° C. to 40° C. Tgs used herein are those determined bydifferential scanning calorimetry (“DSC”).

The inkjet ink binders are typically prepared by emulsionpolymerization. The polymerization techniques used to prepare aqueousemulsion polymers are well known in the art. In the emulsionpolymerization process conventional surfactants may be used such as, forexample, anionic and/or nonionic emulsifiers such as, for example,alkali metal or ammonium salts of alkyl, aryl, or alkylaryl sulfates,sulfonates or phosphates; alkyl sulfonic acids; sulfosuccinate salts;fatty acids; ethylenically unsaturated surfactant monomers; andethoxylated alcohols or phenols. The amount of surfactant used isusually 0.1 % to 6% by weight, based on the weight of monomer. Eitherthermal or redox initiation processes may be used, in any known reactionprocess. Preferred is a reaction temperature between 10° C. and 95° C.,more preferably between 20° C. and 90° C. The monomer mixture may beadded neat or as an emulsion in water. The monomer mixture may be addedin one or more additions or continuously, linearly or not, orcombinations thereof, over the reaction period that is typically from 60to 140 minutes.

Conventional free radical initiators may be used such as, for example,hydrogen peroxide, sodium peroxide, potassium peroxide, t-butylhydroperoxide, cumene hydroperoxide, ammonium and/or alkali metalpersulfates, sodium perborate, perphosphoric acid and salts thereof,potassium permanganate, and ammonium or alkali metal salts ofperoxydisulfuric acid, typically at a level of 0.01% to 3.0% by weight,based on the weight of total monomer. Redox systems using the sameinitiators coupled with a suitable reductant such as, for example,sodium sulfoxylate formaldehyde, ascorbic acid, isoascorbic acid, alkalimetal and ammonium salts of sulfur-containing acids, such as sodiumsulfite, bisulfite, thiosulfate, hydrosulfite, sulfide, hydrosulfide ordithionite, formadinesulfinic acid, hydroxymethanesulfonic acid, acetonebisulfite, amines such as ethanolamine, glycolic acid, glyoxylic acidhydrate, lactic acid, glyceric acid, malic acid, tartaric acid and saltsof the preceding acids may be used. Redox reaction catalyzing metalsalts of iron, copper, manganese, silver, platinum, vanadium, nickel,chromium, palladium, or cobalt may be used. Chelating agents for themetals may optionally be used.

In one embodiment of the present invention the aqueous emulsion polymermay be prepared by a multistage emulsion polymerization process, inwhich at least two stages differing in composition are polymerized insequential fashion. The polymerization techniques used to prepare suchmultistage emulsion polymers are well known in the art such as, forexample, U.S. Pat. Nos. 4,325,856; 4,654,397; and 4,814,373.

The number average particle diameter of the polymer particles istypically from 150 to 400 nm, preferably from 250 to 300 nm, as measuredby Capillary Hydrodynamic Fractionation (“CHDF’). The particle sizedistribution may be unimodal, bimodal, or polymodal; a unimodaldistribution is preferred.

The inkjet ink of the present invention includes the inkjet ink binder;a liquid medium, preferably predominantly water and more preferablydeionized water; and a colorant, such as a dye, pigment, or combinationsthereof, preferably an organic or inorganic pigment. Typically thebinder is present at a level of from 0.1 to 10 wt %, preferably from 2to 3 wt %, based on the total weight of the ink. The aqueous carrier maybe water; preferably, deionized water. Typically the aqueous carrier ispresent at from 40 to 95 wt %, preferably from 55 to 80 wt %, and morepreferably, from 70 to 80 wt % based on the total weight of the ink.

The inkjet ink typically includes a pigment. As a result of the physicalproperties of pigments, pigment based ink compositions have a tendencyto dry smear, have low resistance to wet-rub and have low highlighterresistance. The term “dry smear,” as used herein, means applyingabrasive pressure across the printed substrate and measuring any smearcreated thereby. The term “highlighter resistance,” as used herein,means applying abrasive pressure across the printed substrate with acommercially available highlighting marker and measuring any smearcreated thereby; an example of such marker is Sanford Corp. MAJOR ACCENTbrand highlighting markers.

Suitable pigments include, for example, organic pigments such as azocompounds, phthalocyanine pigments, quinacridone pigments, anthraquinonepigments, dioxazine pigments, indigo, carbon black, thioindigo pigments,perynone pigments, perylene pigments, and isoindolene; and inorganicpigments such as titanium dioxide, iron oxide, and metal powders.Typically the amount of colorant used is less than 10 wt %, preferablyfrom 0.5 to 7 wt %, and more preferably from 3 to 6%, based on the totalweight of the ink. Preferably, the pigment particle size is from 0.05 to5 microns, more preferably not more than one micron and most preferablynot more than 0.3 microns.

The inkjet ink may include a pigment dispersant. Suitable polymericdispersants are known in the art, for example, in U.S. Pat. No.5,821,283, U.S. Pat. No. 5,221,334, U.S. Pat. No. 5,712,338, and U.S.Pat. No. 5,714,538. Alternatively, pigment known as a self-dispersedpigment may be used or mixtures of a self-dispersed pigment and apigment with dispersant. Pigments known as self-dispersed pigments orself-dispersing have been created with a surface modification. Suchpigments can be surface modified in a variety of ways including, but notlimited to, treatment with alkali salts of hypochlorite, ozone, anddiazonium salts of aromatic sulfonic acid additions. These surfacemodified pigments have the distinct advantage of being self-dispersed inaqueous media and can be used without a corresponding polymericdispersing agent. The surface modification can be performed on bothblack and color pigments.

For the purposes of this invention, the polymeric dispersant compositionis not critical as long as its use results in a stable and printableink. Polymeric dispersants are typically used at 0.1 to 5 wt %, based onthe total weight of the ink. Pigment dispersions may be made by mixingpigment, dispersant, water, and optional additives and milling in, forexample, a horizontal media mill, a vertical media mill, and an attritormill.

The inkjet ink may also include, for example, humectants, dispersants,penetrants, chelating agents, buffers, biocides, fungicides,bactericides, surfactants, anti-curling agents, anti-bleed agents andsurface tension modifiers. Useful humectants include ethylene glycol,1,3 propanediol, 1,4 butanediol, 1,4 cyclohexanedimethanol, 1,5pentanediol, 1,2-hexanediol, 1,6 hexanediol, 1,8 octanediol, 1,2propanediol, 1,2 butanediol, 1,3 butanediol, 2,3 butanediol, diethyleneglycol, triethylene glycol, tetraethylene glycol, polyethylene glycolwith average molecular weight of 200, 300, 400, 600, 900, 1000, 1500 and2000, dipropylene glycol, polypropylene glycol with average molecularweight of 425, 725, 1000, and 2000, 2-pyrrolidone,1-methyl-2-pyrrolidone, 1-methyl-2-piperidone, N-ethylacetamide,N-methylpropionamide, N-acetyl ethanolamine, N-methylacetamide,formamide, 3-amino-1,2-propanediol, 2,2-thiodiethanol,3,3-thiodipropanol, tetramethylene sulfone, butadiene sulfone, ethylenecarbonate, butyrolacetone, tetrahydrofurfuryl alcohol, glycerol,1,2,4-butenetriol, trimethylpropane, sorbital, pantothenol, LiponicEG-1. Preferred humectants are polyethylene glycol with averagemolecular weight of 400 to 1000, 2-pyrrolidone 2,2 thiodiethanol, and1,5 pentanediol. The amount of humectant used may range from 1 to 30 wt%, preferably from 5 to 15 wt %, based on the total weight of the ink.Preferred penetrants are 1,2 C₁-C₆ alkyl diols, such as 1,2 hexanediol;N-propanol; isopropanol; and hexyl carbitol. The amount of penetrantused may range from 0.1 to 10 wt %, based on the total weight of theink.

The inkjet ink may be prepared by any method known in the art such as,for example, by mixing, stirring or agitating the ingredients together.

The inkjet ink may be applied to a substrate such as paper, vinyl, andthe like using thermal or piezoelectric inkjet ink printers such as, forexample, Lexmark 7000, Lexmark 5700, Lexmark Z32, Lexmark Z51, LexmarkZ-65, Lexmark 2050 printers, Epson Stylus™ 3000, C-82, C-84,Hewlett-Packard DeskJet™ 550, 570, 694C, 698, 894, 895Ci, and Canon 750.The ink may be allowed to dry at ambient temperature or heated to dry ata higher temperature.

The following examples are illustrative of the invention.

Experimental Methods

The resistance of inks to highlighter smearing is measured by assessingthe optical density of the trailing edge of a highlighter mark afterpassing over the printed substrate into an unprinted area of thesubstrate. Printing reliability is measured by the number of cloggedprint head nozzles after printing 90 pages on a Lexmark desktop printer;values presented are the mean of six trials. The highlighter resistancetest is used for all smear resistance testing.

The number average particle diameter reported herein is that determinedby CHDF using a Matec model-2000 CHDF measurement system with a C-202cartridge and GR-500 (2×) eluant (diluted 1/20). The CHDF instrument iscalibrated with nominal 50, 100, 200, 300, 400, 500, 600, and 700 nmpolystyrene column standards (“Nanosphere™” standards from DukeScientific Corp., Palo Alto, Calif., USA) using the “new sigmoid fit”procedure (Matec CHDF-2000 software, version 3.20). Particle sizes arecalculated using the deconvolution calculation for maximum resolution.

Glass transition temperatures are measured by Differential ScanningCalorimetry with a model Q-1000 DSC instrument (TA Instruments, NewCastle, Del., USA) at a temperature ramp rate of 20° C./minute (afterpre heating the sample to 150° C. for 5 min) on a 16 mg sample in anitrogen atmosphere, using “Universal Analysis” software (version 4.0.0)to calculate the midpoint of the transition.

All ranges disclosed herein are inclusive and the minimums and maximumsof the nested ranges are combinable.

Abbreviations Used Herein

Wt %=weight percent

SLS=sodium lauryl sulfate

NaPS=sodium persulfate

APS=ammonium persulfate

KDDBS=potassium n-dodecyl benzenesulfonate

EA=ethyl acrylate

MMA=methyl methacrylate

MAA=methacrylic acid

AA=acrylic acid

AN=acrylonitrile

BA=butyl acrylate

EHA=2-ethylhexyl acrylate

AAm=acrylamide

DI water=deionized water

EXAMPLE 1 Preparation of Inkjet Ink Binder and Inkjet Ink

To a reaction vessel containing 525 ml DI at 18° C., 20% of a mixture of487 g water, 2.0 g SLS (28%), 72.2 g Triton™ X-165 surfactant (70%),82.9 g AAm; (53% aq.), 115 g AN, and 985 g EA is added along with 2.8 g0.15% ferrous sulfate, 0.48 g APS, and 0.42 g Lykopon™ along with 36 gwater. After the vessel is inerted and stirring applied, the reactiondisplays an exotherm. After the exotherm, the rest of the monomermixture is added gradually after adding an additional 1.26 g of SLS,26.7 g of Triton™ X-165, and 44 g water to the remaining monomeremulsion. The polymerization maintains a temperature of 62-64° C. duringthe monomer addition. A co-feed of 1.6 g APS in 45 g water and 2.2 gsodium bisulfite in 45 g water is also gradually added. Rinses of water(6 g total) are added, and the reaction is gradually cooled to 30° C.,diluted with an additional 147 g water, and filtered. An 800 g portionof the filtered product is neutralized with 1% KOH (pH=8.7), diluted to25% solids with additional water, and filtered through a 1 micron filterto give the final sample. The number average particle size is 206 nm(CHDF) and Tg is +2.6° C. (DSC).

An ink jet ink composition is then prepared with the binder from Example1 by mixing the ingredients as follows: Formulation 1 Ingredient WeightPercent (%) Self-Dispersing Carbon Black 2 Dispersed Carbon Black 2Example 1 binder 3 Polyethylene Glycol 400 7.5 2-Pyrrolidinone 7.51,2-Hexanediol 1.2 Hexylcarbitol 0.4 Water Balance TOTAL 100.0

The ink is used to print on a Lexmark desktop printer. On the 90^(th)page of this print test that is repeated 6 times, an average of 152 (outof 208 nozzles) nozzles in the ink cartridge continues to fire.Performance in terms of wet-rub smear or resistance to smearing byhighlighter pens is excellent, with little-to-no smearing evident. Theaverage particle size of the resin is 281 nm by laser light scatteringmethod; the Tg is +2.6° C.

COMPARATIVE EXAMPLE A Preparation of Comparative Inkjet Ink Binder andInkjet Ink

A monomer mixture is polymerized according to EXAMPLE 1 except that 20%of a mixture of 487 g water, 2.0 g SLS (28%), 72.2 g Triton X-1 65™(70%), 98 g methylol acrylamide-45 (45% solids, Cytec Industries), 115 gAN, and 985 g EA is used in the polymerization. After the reactionmixture is gradually cooled to 30° C., it is diluted with an additional145 g water and filtered. An 800 g portion of the filtered product isneutralized with 1% KOH (pH=8.7), diluted to 25% solids with water, andfiltered through a 1 micron filter to give the final sample. The numberaverage particle size is 226 nm (CHDF), Tg is −1.5° C. (DSC) andby-product free formaldehyde is 139 ppm per gram of emulsion polymer.

The ink formulation is identical to that of Formulation 1 using thebinder of Comparative Example A. The ink is used to print 90 pages on aLexmark desktop printer. On the 90^(th) page of this print test that isrepeated 6 times, an average of 191 (out of 208 nozzles) nozzles in theink cartridge continues to fire. Performance in terms of resistance tosmearing by highlighter pens is similar to that of Example 1.

COMPARATIVE EXAMPLE B Preparation of Comparative Inkjet Ink Binder andInkjet Ink

To a reaction vessel containing 533 ml DI water 2.8 g 0.15% ferroussulfate, 0.48 g APS, 0.42 g Lykopon™, and 101 g of an acrylic polymerdispersion (average particle size=99 nm, 45% solids) to 18° C. andinerting the vessel with nitrogen, 34% of a mixture of 487 g water, 7.1g of SLS (28%), 115 g AN, and 1030 g EA is slowly added with stirringalong with 36 g water. After a period of time, the reaction displays anexotherm. After the exotherm, the rest of the monomer mixture isgradually added, along with 36 g water. A co-feed of 1.6 g APS in 45 gwater and 2.2 g sodium bisulfite in 45 g water is also added over themonomer feed period. The polymerization is maintained at a temperatureof 62-64° C. during the monomer addition. Additional rinses of water (6g total) are added, and the reaction is gradually cooled to 30° C.,diluted with 125 g water, and filtered. An 800 g portion of the filteredproduct is neutralized with 1% KOH (pH=7.3), diluted to a 25% solidslevel with additional water, and filtered through a 1 micron filter togive the final sample. The number average particle size is 280 nm(CHDF), and Tg is +3.0° C. (DSC).

An ink (Formulation 1 with the binder of Comparative Example B) is usedto print on a Lexmark desktop printer. On the 10^(th) page of this printtest that is repeated 6 times, an average of 0 (out of 208 nozzles)nozzles in the ink cartridge continues to fire. Performance in terms ofresistance to smearing by highlighter pens is similar to that of Example1.

EXAMPLE 2 Preparation of Inkjet Ink Binder and Inkjet Ink

A monomer mixture is polymerized according to Comparative Example Bexcept that 33% of a mixture of 487 g water, 7.1 g of SLS (28%), 82.8 gAAm (53% aq.), 240 g MMA and 859 g BA is gradually added to a reactionvessel containing 531 ml deionized water along with 36 g water. Thereaction mixture is gradually cooled to 30° C., diluted with anadditional 89 g water, and filtered. An 800 g portion of the filteredproduct is neutralized with 1% KOH (pH=7.1), diluted to 25% solids withadditional water, and filtered through a 1 micron filter to give thefinal sample. The number average particle size is 260 nm (CHDF), and Tgis −23° C. (DSC).

An ink (Formulation 1 with the binder of Example 2) is used to print ona Lexmark desktop printer. On the 90^(th) page of this print test thatis repeated 6 times, an average of 107 (out of 208 nozzles) nozzles inthe ink cartridge continues to fire. Performance in terms of resistanceto smearing by highlighter pens is inferior to that of Example 1.

EXAMPLE 3 Preparation of Inkjet Ink Binder and Inkjet Ink

A monomer mixture is polymerized according to Comparative Example Bexcept that 34% of a mixture of 487 g water, 7.1 g of SLS (28%), 82.9 gAAm (53% aq.), and 10 g EA is gradually added to a reaction vesselcontaining 526 ml DI water along with 36 g water. The reaction isgradually cooled to 30° C., diluted with an additional 93 g water, andfiltered. An 800 g portion of the filtered product is neutralized with1% KOH (pH=7.1), diluted to 25% solids with water, and filtered througha 1 micron filter to give the final sample. The number average particlesize is 274 nm (CHDF), and Tg is −10.9° C. (DSC).

An ink (Formulation 1 with the binder of Example 3) is used to print ona Lexmark desktop printer. On the 90^(th) page of this print test thatis repeated 6 times, an average of 180 (out of 208 nozzles) nozzles inthe ink cartridge continues to fire. Performance in terms of resistanceto smearing by highlighter pens is equivalent to that of Example 1 withlittle-to-no smearing evident.

COMPARATIVE EXAMPLE C Preparation of Comparative Inkjet Ink Binder andInkjet Ink

A monomer mixture is polymerized according to Comparative Example Bexcept that 34% of a mixture of 487 g water, 7.1 g of SLS (28%), and1144 g EA is gradually added to a reaction vessel containing 533 ml DIwater along with 36 g water. The reaction is gradually cooled to 30° C.,diluted with 125 g water, and filtered. An 800 g portion of the filteredproduct is neutralized with 1% KOH (pH=7.0), diluted to a 25% solidslevel with water, and filtered through a 1 micron filter to give thefinal sample. The number average particle size is 277 nm (CHDF), and Tgis −14.1° C. (DSC).

An ink (Formulation 1 with the binder of Comparative Example C) is usedto print on a Lexmark desktop printer. At or near the first page of thisprint test, all nozzles are clogged, giving an average of 0 (out of 208nozzles) nozzles in the ink cartridge that continues to fire.Performance in terms of resistance to smearing by highlighter pens isequivalent to that of Example 1 with little-to-no smearing evident.

1. An inkjet ink binder comprising an aqueous dispersion of polymerparticles, said polymer comprising, as polymerized units, (a) from 0 to1 wt. % monoethylenically unsaturated acid monomer, based on polymerweight; and (b) monomer of the formulaCH₂═C(R1)—CON(R2)(R3) wherein R1═H, CH₃ or C₂H₅ and R2 and R3 areindependently selected from C1-C6 saturated alkyl and cycloalkyl groups;and wherein the total of (a) and (b) is at least 0.1 wt % monomer basedon said polymer weight.
 2. The inkjet ink binder of claim 1 furthercomprising, as polymerized units, from 10 to 98 wt %, C1-C3 alkylacrylate.
 3. The inkjet ink binder of claim 1 wherein monomer (b) isselected from the group consisting of acrylamide, methacrylamide,ethacrylamide, N-methyl acrylamide, N-ethyl methacrylamide, N-t-butylacrylamide, N,N-dimethyl acrylamide, N-cyclohexyl acrylamide, andcombinations thereof.
 4. The inkjet ink binder of claim 1 wherein theglass transition temperature of the binder is in the range of −40° C. to120° C.
 5. The inkjet ink binder of claim 1 wherein the number averageparticle diameter of the polymer particles is from 150 to 400 nm, asmeasured by Capillary Hydrodynamic Fractionation (“CHDF”).